Here is a patch with smaller (in comparison with issue27358) change for 3.5 that improves error message when pass a non-mapping as second var-keyword argument.

Unpatched:

>>> f(**{'a': 1}, **[])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'list' object is not a mapping
>>> f(**{'a': 1}, **0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable

Patched:

>>> f(**{'a': 1}, **[])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() argument after ** must be a mapping, not list
>>> f(**{'a': 1}, **0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: f() argument after ** must be a mapping, not int